Time-dependent changes in intracellular ROS formation, extracellular nitrite concentration, and CD40 expression in human cultured endothelial cells exposed to cyclic stretch. (A) Time course of ROS formation shown as statistical summary of the relative changes in DCF fluorescence (●, n = 3-4, *P < .05 vs 0 hours). NOS-3 enzyme activity was estimated on the basis of the nitrite content of the conditioned medium (○, n = 4-8, *P < .05 vs 0 hours). (B) Time course of CD40 mRNA (○, n = 4-8, *P < .05 vs 0 hours) and CD40 protein abundance (●, n = 4-12; *P < .05 vs 0 hours) in the cultured cells, as judged by PCR and Western blot analysis, respectively. Changes in CD40 expression are calculated as percentage of the mRNA or protein level in nonstretched cells (basal).